When we first launched https://www.Feastflow.com, a handcrafted lead gen service for freelance developers, we didn't offer a free trial or a money back guarantee and we got a lot of feedback that it was necessary. This might be a different perspective since we are a subscription service but having a "no questions asked" 30 day refund policy has definitely boosted our conversion and led to a much larger userbase. We found that our biggest sticking point was getting a user to give us a try and after experiencing the quality of our leads there is very little chance they ask for a refund.